When a person's larynx has been removed by surgery due to pathological changes in the throat, the trachea of the person is sutured to an opening in the throat. This is called a tracheostoma. By the surgery the person has lost the ability to speak, and in order to restore this ability a voice prosthesis of the kind referred to above is mounted in a fistula, i.e. a passage between trachea and esophagus. At speech the tracheostoma is occluded by sealing the same either by the patient placing the fingers against the tracheostoma or by the tracheostoma being closed via a tracheostoma valve arranged in connection with the tracheostoma valve. Then, the expiration air is pressed from the lungs through the voice prosthesis into esophagus. Here the mucous membranes of the throat of the person are brought into vibration and speech is produced as a consequence thereof.
Existing voice prostheses have in common that they normally provide a check valve function, which means that the valve member normally is closed but opens when air is pressed from trachea via the valve member to esophagus. The valve member is maintained in the closed position by spring bias which in most cases is maintained by elasticity of the material from which the voice prosthesis is made.
The function of such voice prostheses is initially acceptable, but they tend to have short life span, since growth of candida most often occurs at the sealing surfaces of the valve member and the corresponding valve seat, causing leakage from the esophagus into the trachea, and the spring bias is lost, also this resulting in a leakage through the voice prosthesis from the esophagus into the trachea.
U.S. Pat. No. 7,166,128 discloses a voice prosthesis of this kind, wherein a permanent magnet is arranged at the valve member or the valve seat, and a permanently magnetically attracting material is arranged on the opposite side, i.e. the one of the valve member and the valve seat not being provided with the permanent magnet, to alleviate the problem of lost spring bias. The problem of candida formation is alleviated with the use of a candida resistant material on the valve member. However, since candida still will be formed adjacent the valve member and on the valve seat, as well as to some degree accumulate on the valve member, even though it does not grow into the candida resistant material, the valve member will not be able to close entirely against the valve seat, regardless of magnetic attraction between the valve member and the valve seat. Also, candida formed in the vicinity of the valve/valve seat may en up at the valve/valve seat, together with mucus, food, etc., which may cause a leakage until it is removed.